13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- An Equivalent Strain Gradient Theory for Evolvement of Damage in void Material Hong Zuo*, Fangwen Wang* &Teng Hou State Key Laboratory of Mechanical Structure Strength and Vibration, School of Aerospace, Xi’an Jiaotong Univ. Xi’an, PR. China * Corresponding author: Email: zuohong@mail.xjtu.edu.cn; fwwang@mail.xjtu.edu.cn Abstract In this article, the onset conditions and evolvement path of the crack initiated from void edge in void material are investigated. For this end, the plane stress numerical simulation is implemented for a series of void embedded strip samples in Al-alloy. The stress and strain distribution for the whole plane sample is analyzed by elastic-plastic FEM. Based on the correspondence between equivalent strain distributions, the trend of equivalent strain gradient and the connected style of voids in experiment, a damage evolvement theory for the crack initiation and extension from vole edge is suggested. According to the suggested theory, as the loading increased, the crack is initiated from the edge of the void where the equivalent strain around the edge of the void reached its maximum; next, the initiated crack will propagated along the direction where the absolute gradient value of equivalent strain reached its maximum. It is indicated from the related experiments that the theory can reasonably explain the phenomena of the different linkage style of two holes. Keywords void material; path of the crack extension; equivalent strain grade; voids converge. 1. Introduction In practical structure, the damage or degradation of material is usually the fatal factor influencing the reliability of mechanical engineering structure. However, from microscopic view, the damage in macroscopic is always induced by the accumulation of a series of voids converge, i.e., the voids nucleation, expansion and convergence under loading. Although the crack problem has been paid great attention by mechanical scientists in fracture mechanics field near a century, a lot of fracture theory and criteria had been proposed to describe the mechanisms of crack initiation and extension. However, the void convergence problem has received fewer attentions relatively till today. Especially in the problem of convergence process of voids, much less for the theory. Only fewer studies related to the void convergence can be retrieved from the open literatures. Most of them are concentrated to the numerically simulation for the void expension and convergence and other factors such as size and direction of grain [1-4]. Thereby, thoroughly understanding the mechanism of the linkage of voids is the precondition for the processing of material and the reliability of structure during its operation. However, the process of the voids linkage under practical stress state is rather complicated considering the relation between relative location of voids and the stress direction. In this article, the problem is simplified to study the void linkage mechanism and control parameter for a multi-hole embedded plate under single loading condition.
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